Something supernatural is something that is outside scientific understanding of nature, for example witchcraft that goes against what is physically possible within what we know about the universe. Or it could be something that exists outside the dimensions of space and time for example ghosts or god, with the exception of consciousness. Which is why I would say something like bigfoot is not supernatural. The problem that I can see with this question is that anything supernatural has no good evidence for you to believe that it exist within reality, and everything supernatural is only supernatural because it is something that can not be proved to exist, and anything supernatural that was proved to exist, would no longer be called supernatural, just a natural phenomena that has not yet been explained by science. This is why many things that used to be considered supernatural, are now natural.